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The present invention relates to color systems and, more particularly, to a method and system for transforming a color palette with TV unsafe colors into a palette that contains only TV safe colors in such a way that the initial and transformed color palettes are nearly identical when perceived by the human eye.
The range or gamut of colors that a television system can transmit and display is limited. Standards of the NTSC (National Television Systems Committee) system used throughout North America, and other television system standards, determine which colors are xe2x80x9csafexe2x80x9d for transmission and display on a television set and which are xe2x80x9cunsafe.xe2x80x9d This contrasts with the color gamut supported by computer systems such as personal computers, which typically support the use of a color gamut ranging from 256 colors to millions of distinct colors. Indeed, it is common for 25 percent or more of the colors in a typical computer system source palette (the selection of colors from which colors may be selected for images) to be TV unsafe, and many computer graphic images contain colors which cannot be supported in a television signal.
The convergence of computers and television makes it desirable to be able to display graphical color information created for a computer on a television. There are a variety of models and methods commonly used in the industry to assure the TV safeness of colors in computerized graphic images. One method is to simply avoid the use of TV unsafe colors altogether, which often has the effect of eliminating 25 percent or more of the colors in a source color palette. This limits the range of colors even when the image is available for viewing on a computer system. A second method in use is a model whereby TV unsafe colors in the source palette are forced to be TV safe while TV safe colors are unaltered. As a result, the color trends and interrelationships of the original palette are destroyed. A third model in use is one where all RGB values are scaled by a single factor to assure TV safeness. While this method has the benefit of maintaining the color trends of the source palette, they are maintained at the expense of over attenuating a significant amount of colors in the source palette.
The above approaches are simplistic solutions to the problems associated with graphic images and TV color safety. These approaches, however, generally fail to accomplish what should be intuitive goals of color palette translation, such as keeping the number of colors in the translated palette equal to the number of colors in the source palette, altering the colors in the source palette only as much as is required to make them TV safe, and maintaining the color trends of the source palette. There is thus a need for techniques more directed to achieving these goals. The techniques presented herein offer a method for translating color palettes for use in television systems that is superior to those that currently exist in the field of color transformation.
It is an object of the present invention to solve the problems described above with existing color translation systems.
It is another object of the present invention to transform a color palette with TV unsafe colors into a palette that contains only TV safe colors in such a way that the initial and transformed color palettes are nearly identical when perceived by the human eye.
It is another object of the present invention to perform such a color transformation while preserving the number of colors in the source palette for other applications.
It is another object of the present invention to perform such a transformation while maintaining the color trends of the initial palette.
The color palette translation model discussed herein, however, can be extended to any television system. Essentially, the model presented herein consists of four main steps:
(1) Determination of the TV unsafe colors in the source color palette;
(2) Replacement of the TV unsafe colors with optimal TV safe colors;
(3) Segmentation of color space into color regions;
(4) Modification of all other source palette colors based on operations performed on the TV unsafe colors in Step (2) and the color space regions defined in Step (3).
By applying this method to a color palette containing colors unfit for display on a television set, a palette is generated that contains only TV safe colors. Moreover, the resultant palette is created in such a way that the initial and transformed color palettes are nearly identical when perceived by the human eye.